Spark ignition systems



Aug. 12, 1969 B. GILBERT 3,461,345

SPARK IGNITION SYSTEMS Filed June 6, 1962 2 Sheets- Sheet 1 Aug. 12, 1969 B. GILBERT 3,461,345

SPARK IGNITION SYSTEMS Filed June '6, 1962 2 Sheets-Sheet 2 United States Patent 3,461,345 SPARK IGNITION SYSTEMS Brian Gilbert, Sutton Coldfield, England, assignor to Joseph Lucas (Industries) Limited, Birmingham, England Filed June 6, 1962, Ser. No. 200,449 Claims priority, application Great Britain, June 13, 1961, 21,243/ 61 Int. Cl. H]: 41/36 US. Cl. 315--209 11 Qlaims This invention relates to spark ignition systems for internal combustion engines, of the kind in which current flow in a winding controls discharge across a spark plug of the engine.

The winding may be the primary winding of a transformer having the plug in its secondary circuit. How ever, where low-voltage plugs are used the plug may be connected directly across the winding.

The present invention makes use of a device known as a controlled rectifier, the characteristic of which is that if a triggering pulse is applied between its gate and cathode terminals the rectifier becomes conductive, and thereafter continues to conduct, even when the triggering pulse is removed, until the anode-cathode current falls practically to zero. Furthermore, it has recently been discovered that controlled rectifiers manufactured in a certain manner have the additional property that they can be switched off by a pulse of opposite polarity (but not necessarily of equal magnitude) applied between the gate and cathode. Throughout this specification the term switchable rectifier is used to mean a controlled rectifier having this additional property, a convenient method of manufacturing a switchable rectifier being described in pending application No. 211,674, now US. Patent No. 3,223,560.

According to the invention, a spark ignition system of the kind specified includes a switchable rectifier for controlling current flow through the winding, and means operable in use to successively switch the switchable rectifier on and off by applying positive and negative pulses to its gate.

In the accompanying drawings:

\FIGURE 1 is a circuit diagram illustrating one example of the invention, the transformer secondary circuit shown in FIGURE 1 being common to all the figures and omitted in the remaining figures;

FIGURE 2 illustrates a modification of the example seen in Figure 1; i

FIGURE 3 is a diagram illustrating a circuit similar to that shown in FIGURE 2;

FIGURE 4 illustrates a further modification of FIG- URE 1;

\FIGURE 5 illustrates another example of a suitable circuit and FIGURE 6 is a circuit diagram illustrating a modification of FIGURE 5.

Referring first to FIGURE 1, there is provided a transformer 11 having its secondary Winding 12 connected through a distributor 13 to the spark plugs 14 of an engine. One end of the primary winding 15 of the transformer is connected to the positive terminal 16 of a twelve volt battery 17, whilst its other end is connected to the negative terminal 18 of the battery through the anode and cathode of a switchable rectifier 19. The latter is bridged by a capacitor 20, and any convenient means is provided for supplying successive pulses of opposite polarity to the gate of the rectifier 19. Thus, the gate may be connected to the terminal 18 through :a second capacitor 21 and a resistor 22, a point intermediate the capacitor 21 and resistor 22 being connected to the terminal 16 through an engine-driven interrupter 23.

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In operation, closing of the interrupter 23 causes a positive pulse to be supplied through the capacitor 21 to the gate of the rectifier 19, so that current flows in the primary winding 15. On opening of the interrupter 23, the discharging of the capacitor 21 through the resistor 22 causes a negative pulse to be applied to the gate to render the rectifier 19 nonconductive. The resultant fall in current in the primary winding 15 causes a large voltage to be induced in the secondary winding 12, a discharge then taking place across a plug 14 in known manner. The purpose of the capacitor 20 is to protect the rectifier 19 from damage by surges of current, although in some applications the self-capacitance of the rectifier 19 may be adequate for this purpose.

In a minor modification of this example, the positions of the interrupter 23 and resistor 22 are reversed. In this case, opening of the interrupter 23 switches the rectifier 19 on, and closing of the interrupter 23 switches the rectifier 19 off. The modification is best suited to negative earth systems, whilst the example shown in FIG- URE 1 is more useful for positive earth systems.

Referring now to FIGURE 2, the example there shown is similar to that shown in FIGURE 1, and equivalent parts have been designated with the same reference numerals. However, in this example an inductor 24 is included in series with the resistor 22, and the interrupter 23 is bridged by a capacitor 25. Further, second and third resistors 26, 27 are included in series and in parallel respectively with the capacitor 21. In this example, opening of the interrupter 23 causes a negative pulse to be applied to the gate as before, the effect being enhanced by the inductor 24. The resistors 26, 27 serve to shape the pulse applied to the gate, and the capacitor 25 limits arcing between the contacts of the interrupter 23.

The example shown in FIGURE 3 differs from that shown in FIGURE 2 in that the capacitor 21 and resistors 22, 27 are omitted, additional resistors 28, 29*being included in series with the interrupter 23 and the winding 15 respectively, and a resistor 30 connecting the terminal 18 to the gate of the rectifier 19. In operation, on closing the interrupter 23 a positive current flows to the gate to switch the rectifier 19 on. The current flow in the gate reduces as the current flowing to the inductor 24 builds up, until in the steady state only a small current flows in the gate. Upon opening of the interrupter 23, the energy stored in the inductor 24 serves to switch off the rectifier 19. Preferably, a diode 32 is connected across the resistor 26 to prevent needless waste of the energy stored in the inductor 24.

When the interrupter 23 opens, the capacitor 25 is charged while the rectifier 19 is switched off. When the rectifier 19 is off, the capacitor 25 discharges and may possibly switch the rectifier 19 on again. This can be prevented by including a diode 31 in series with the resistor 28, and connecting a resistor across the capacitor 25 to provide a discharge path therefor. Alternatively, the circuit may be designed to ensure that discharge of the capacitor switches the rectifier 19 on instead of closing of the interrupter 23, thereby lengthening the time available for storing energy in the Winding 15.

Turing now to FIGURE 4, the example there shown differs from that shown in FIGURE 1 in that an itnerrup-ter 33 is included in series with the resistor 22, and a resistor 34 is included in series with the interrupter 23. Moreover, resistors 29, 30 are included as in FIGURE 3.

The interrupters 23, 33 are designed to operate out of phase, so that they are never closed together. For this purpose they may conveniently be incorporated in a single lever. The operation is similar to the circuit shown in 3 FIGURE 1, the resistors 22, 34- permitting independent adjustment of the magnitude of the switch-011 and switchoff currents.

In the example shown in FIGURE 5, one end of the primary winding 15 is connected to the terminal 18 and the other end is connected to the terminal 16 through a capacitor 35, a diode 36 and an inductor 37. The rectifier 19 is connected across the capacitor 35 and the primary winding 15. The gate circuit may take a variety of forms, but is shown similar to that illustrated in FIGURE 1. If desired, the diode 36 can be placed the other side of the inductor 37.

In operation, the gate is supplied with successive positive and negative pulses as in the example described with reference to FIGURE 1. When the gate receives a negative pulse, energy stored in the inductor 37 charges the capacitor 35, which is prevented from discharging by the diode 36. When a positive pulse is received by the gate terminal, the rectifier 19 conducts and the capacitor 35 discharges rapidly through the winding 15, thereby inducing a high voltage in the secondary winding 12. Energy is again stored in the inductor 37 while the rectifier 19 is conducting.

In a modification of FIGURE 5, a second interrupter is included between the diode 36 and capacitor 35 and is bridged by a further diode. The purpose of these components is to ensure that it, due to a fault, the interrupter 23 recloses transiently after opening, a spark will not be generated. The second interrupter operates in advance of the interrupter 23 and closes a predetermined period of time after the interrupter 23 opens. Hence, during this delay period there is no connection between the capacitor 35 and the rectifier 19, an re-closing of the interrupter 23 has no effect.

In the modified FIGURE seen in FIGURE 6, the gate circuit has been replaced by the gate circuit seen in FIG- URE 3. In this case, it is advantageous to connect capacitors 41, 42 across the resistors 26, 28. These capacitors have been found to improve sparking performance. Furthermore, a diode 43 is connected across the winding so that current flowing to charge the capacitor 35 is not impeded by the winding 15, and a diode 44 is connected across the anode and cathode of the rectifier 19 to protect the latter. Moreover, a capacitor 45 is connected across the rectifier 19 to protect the latter, and a resistor 46 is included in series with the inductor 37.

In each of the examples described an interrupter has been employed, and acts as an engine-controlled switch. In every case, however, the interrupter could be replaced by a semi-conductor switch controlled by magnetic or other means associated with the engine.

The ignition transformer circuit described is conventional, and could be replaced in certain instances by a system employing separate ignition transformers for each plug. In this case the distributor must be in the primary circuit. Moreover, the circuit can be used with lowtension surface discharge plugs, in which case no ignition thransformer is required and the voltage developed across the inductor 15 is applied directly to the plugs in turn.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

l. A spark ignition system for an internal combustion engine having at least one spark plug, comprising a D.C. source, a winding, means whereby current flow in said winding controls discharge across said spark plug, a series circuit connected across said source and including an inductor, 'a diode. a capacitor and said winding, a switchable rectifier having an anode, a cathode and a gate, the anode and cathode being connected to said source in series with said diode and said inductor, said switchable rectifier being switched on by a positive pulse applied between its gate and cathode and being switched oil? by a negative pulse applied between its gate and cathode, a circuit connecting said gate to the D.C. source. an engine-controlled switch in said circuit, operation of said switch by the engine causing successive positive and negative pulses to be applied to said gate to switch the switchable rectifier on and off, said inductor storing energy and said capacitor discharging through said winding to produce said discharge when the switchable rectifier is on, and the energy stored in said inductor serving to charge said capacitor when the switchable rectifier is olf.

2. A spark ignition system as claimed in claim 1 including a diode connected across said Winding to conduct the charging current of said capacitor.

3. A spark ignition system as claimed in claim 1 including a diode having its cathode connected to the anode of said switchable rectifier, and its anode connected to the cathode of said switchable rectifier, said diode permitting an oscillating discharge of said capacitor.

4. A spark ignition system as claimed in claim 1, including a capacitor connected between the anode and cathode of said switchable rectifier.

5. A spark ignition system for an internal combustion engine have at least one spark plug, comprising a D.C. source, a winding connected to said source, means whereby current flow in said winding controls discharge across said spark plug, a switchable rectifier having an anode, a cathode and a gate, said switchable rectifier being switched on by a positive pulse applied between its gate and cathode and being switched olf by a negative pulse applied between its gate and cathode, a series circuit connected across said D.C. source, said series circuit including an engine-controlled switch and an inductor, means including a resistor bridged by a diode connecting a point intermediate said switch and said inductor to said gate, operation of said switch by the engine causing successive positive and negative pulses to be applied to said gate to switch the switchable rectifier on and cit, and means connecting the anode and cathode of said switchable rectifier in circuit with said winding, switching on and switching off of the switchable rectifier controlling fiow of current in said winding.

6. A spark ignition system as claimed in claim 5 in which said diode is bridged by a capacitor.

7. A spark ignition system for an internal combustion engine have at least one spark plug, comprising a D.C. source, a winding connected to said source, means whereby current fiow in said Winding controls discharge across said spark plug, a switchable rectifier having an anode, a cathode and a gate, said switchable rectifier being switched on by a positive pulse applied between its gate and cathode and being switched off by a negative pulse applied between its gate and cathode, a series circuit connected across said D.C. source, said series circuit including an engine-controlled switch and an inductor, means including a resistor in series with a parallel combination of a capacitor and another resistor connecting a point intermediate said switch and said inductor to said gate, operation of said switch by the engine causing successive positive and negative pulses to be applied to said gate to switch the switchable rectifier on and off, and means connecting the anode and cathode of said switchable rectifier in circuit with said winding, switching on and switching off of the switchable rectifier controlling flow of current in said winding.

8. A spark ignition system for an internal combustion engine having at least one spark plug, comprising a D.C. source, a winding connected to said source, means whereby current flow in said winding controls discharge across said spark plug, a switchable rectifier having an anode, a cathode and a gate, said switchable rectifier being switched on by a positive pulse applied between its gate and cathode and being switched off by a negative pulse applied between its gate and cathode, a series circuit connecting said gate to the negative terminal of said D.C. source, said series circuit including a first resistor and an inductor, a circuit connecting a point intermediate said first resistor and inductor to the positive terminal of said D.C. source, sad circuit including a diode, a resistor and an engine-driven interrupter, and a capacitor bridging said interrupter, closing of said interrupter causing a positive pulse to be applied to said gate to switch said switchable rectifier on, and opening of said interrupter causing the energy stored in said inductor to be applied to said gate to switch the switchable rectifier off, switching on and switching off of the switchable rectifier controlling flow of current in said winding.

9. A spark ignition system for an internal combustion engine having at least one spark plug, comprising a DC source, a winding, means whereby cur-rent flow in said winding controls discharge across said spark plug, a series circuit connected across said source and including a first inductor, a first diode, a first capacitor and said winding, a switchable rectifier having an anode, a cathode and a gate, the anode and cathode being connected to said source in series with said first diode and said first inductor, said switchable rectifier being switched on by a positive pulse applied between its gate and cathode and being switched off by a negative pulse applied between its gate and cathode, a series circuit connecting said gate to the negative terminal of said D.C. source, said series circuit including a first resistor and a second inductor, a circuit connecting a point intermediate said first resistor and second inductor to the positive terminal of said source, said circuit including a second diode, a second resistor and an engine-driven interrupter, and a second capacitor connected across said interrupter, closing of said interrupter causing a positive pulse to be applied to said switchable rectifier to switch it on, and opening of said interrupter causing the energy stored in said inductor to he applied to said gate to switch the switchable rectifier off, said first inductor storing energy and said first capacitor discharging through said winding to produce said discharge when the switchable rectifier is on, and the energy stored in said first inductor serving to charge said first capacitor when the switchable rectifier is off.

10. A spark ignition system for an internal combustion engine having at least one spark plug, comprising a DC. source, a winding, means whereby current flow in said winding controls discharge across said spark plug, a series circuit connected across said source and including an inductor, a diode, a capacitor and said winding, a switchable rectifier having an anode, a cathode and a gate, the anode and cathode being connected to said source in series with said diode and said inductor, said switchable rectifier being switched on by a positive pulse applied between its gate and cathode and being switched ofi by a negative pulse applied between its gate and cathode, a second series circuit connected across said source and including an engine-driven interrupter and a resistor, and a capacitor connected between said gate and a point intermediate said resistor and interrupter, operation of said interrupter by the engine causing successive positive and negative pulses to be applied to said gate to switch the switchable rectifier on and off, said inductor storing energy and said capacitor discharging through said winding to produce said discharge when the switchable rectifier is on, and the energy stored in said inductor serving to charge said capacitor when the switchable rectifier is 05.

11. A spark ignition system for an internal combustion engine having at least one spark plug, comprising a DC. source, a winding connected to said source, means whereby current flow in said winding controls discharge across said spark plug, a switchable rectifier having an anode, a cathode and a gate, said switchable rectifier being switched on by a positive pulse applied between its gate and cathode and being switched off by a negative pulse applied between its gate and cathode, a capacitor having one side thereof connected to said gate, a first enginedriven interrupter and a tfirst resistor connected between the other side of said capacitor and the positive terminal of said source, a second engine-driven interrupter and a second resistor connected between said other side of the capacitor and the negative terminal of said source, means operable by the engine 'for operating said interrupters so that when one interrupter is closed the other is open and when said one interrupter is open the other interrupter is closed, operation of said interrupters causing successive positive and negative pulses to be applied to said gate to switch the switchable rectifier on and off, and means connecting the anode and cathode of said switchable rectifier in circuit with said winding, switching on and switching oif of the switchable rectifier controlling flow of current in said winding.

References Cited UNITED STATES PATENTS 2,968,296 1/1961 Kaehni 315209 3,045,148 7/1962 McNulty et al 30788.5 3,184,653 5/1965 Hutson 3152D9 3,213,320 10/1965 \Vorrell 315209 JOHN W. HUCKERT, Primary Examiner JERRY D. CRAIG, Assistant Examiner US. Cl. X.R. 

1. A SPARK IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE HAVING AT LEAST ONE SPARK PLUG, COMPRISING A D.C. SOURCE, A WINDING, MEANS WHEREBY CURRENT FLOW IN SAID WINDING CONTROLS DISCHARGE ACROSS SAID SPARK PLUG, A SERIES CIRCUIT CONNECTED ACROSS SAID SOURCE AND INCLUDING AN INDUCTOR, A DIODE, A CAPACITOR AND SAID WINDING, A SWITCHABLE RECTIFIER HAVING AN ANODE, A CATHODE AND A GATE, THE ANODE AND CATHODE BEING CONNECTED TO SAID SOURCE IN SERIES WITH SAID DIODE AND SAID INDUCTOR, SAID SWITCHABLE RECTIFIER BEING SWITCHED ON BY A POSITIVE PULSE APPLIED BETWEEN ITS GATE AND CATHODE AND BEING SWITCHED OFF BY A NEGATIVE PULSE APPLIED BETWEEN ITS GATE AND CATHODE, A CIRCUIT CONNECTING SAID GATE TO THE D.C. SOURCE. AN ENGINE-CONTROLLED SWITCH IN SAID CIRCUIT, OPERATION OF SAID SWITCH BY THE ENGINE CAUSING SUCCESSIVE POSITIVE AND NEGATIVE PULSES TO BE APPLIED TO SAID GATES TO SWITCH THE SWITCHABLE RECTIFIER ON AND OFF, SAID INDUCTOR STORING ENERGY AND SAID CAPACITOR DISCHARGING THROUGH SAID WINDING TO PRODUCE SAID DISCHARGE WHEN THE SWITCHABLE RECTIFIER IS ON, AND THE ENERGY STORED IN SAID INDUCTOR SERVING TO CHARGE SAID CAPACITOR WHEN THE SWITCHABLE RECTIFIER IS OFF. 